The present invention relates to a fiber structure electrode framework of metallized plastic fibers with reinforced edge and welded-on, current-conducting lug.
For connecting fiber structure electrode frameworks of metallized plastic fibers, for example, of nickel-plated polyolefin-felt or -fleece material, it is known to slot the edge of the electrode framework, to insert into the slot the current-conducting lug and then to weld together the electrode framework with the current lug. However, such a possibility is very expensive and realizable only with small quantities.
For connecting current-conducting lugs with fiber structure-electrode frameworks, it is also known to weld together the edge of the electrode framework reinforced by a galvanically deposited metal layer with the current-conducting lug (DE-PS No. 31 42 091). As the fiber structure electrodes have a high capacity in relation to surface with simultaneous very high current load, the current lug must be selected relatively thick for reasons of electric conducting ability (about 1 to 1.5 mm.). The welding together of the current lug with the edge of the fiber structure-electrode framework takes place by resistance welding. For that purpose the fiber structure-electrode framework is placed on the current lug and is welded together with the same under pressure. Disadvantageous with this type of connection is the fact that the bottom edge of the current lug is pressed into the nickel-plated framework and may lead thereat to cracking in the fiber framework. Additionally, the supporting cross section of the framework is strongly reduced at this place. This leads to a low strength of the welded connection so that during the following operating steps for manufacturing the electrode (installation of the active mass, welding together into plate sets) high reject numbers result owing to breaking off current-conducting lugs. Additionally, during the operation of such cells, particularly with traction utilization, individual plates may break off from the lugs, owing to the mechanical stresses and may lead therewith to failures.
The present invention is therefore concerned with the task to find a fiber structure-electrode framework of metallized plastic fibers with welded-on current-conducting lug, in which no crack formation can occur in the fiber structure-electrode framework in proximity of the welded connection, in which the cross section of the fiber structure-electrode framework is not excessively constricted outside of the reinforced edge and in which the welded connection exhibits a high strength not only when subjected to tensional loads but also in the cross direction and thus enables the manufacture of electrodes with favorable electrical transfer resistances and long service life so that the same can also be utilized in traction batteries.
The underlying problems are solved according to the present invention in that the fiber structure-electrode framework has a thickness of 1 to 10 mm., in that the current-conducting lug is provided with one or several steps along the side abutting at the fiber framework whose height corresponds altogether to 0.3 to 0.8 times the current-conducting lug thickness and whose depth amounts altogether to 3 to 10 mm., in that the edge of the fiber structure-electrode framework is located within an area on the current-conducting lug whose boundaries are located at a distance of twice the current-conducting lug thickness on both sides of the step edge and in that the fiber structure-electrode framework compressed within the stepped area reaches its full thickness approximately continuously up to the end of the step.
The current-conducting lug is provided with one or several steps at the side abutting at the fiber framework whose height corresponds altogether to 0.3 to 0.8 times the lug thickness and whose depth amounts altogether to 3 to 10 mm.
The edge of the fiber structure-electrode framework which is to have a thickness between 1 and 10 mm. may be located inside an area of the current-conducting lug whose boundaries are located at a distance twice the lug thickness on both sides of the step edge. It is preferred when this distance corresponds approximately to the thickness of the current-conducting lug and the fiber framework comes to lie on the stepped-off part of the current-conducting lug. If the fiber framework is located too far from the step, then an excessively high voltage loss will result after the welding operation on the now excessively long unwelded part of the stepped lug. If the fiber framework lies too far on the non-stepped part of the current-conducting lug, then the effect by the step is lost. During the contact pressure of the welding electrodes, the maximum pressures occur in the zone of the reinforced edge of the fiber framework and the welded connection takes place in the preferred embodiment in the first instance in the stepped area of the current-conducting lug. The height of the step is to correspond to 0.3 to 0.8 times the current-conducting lug thickness. It is also possible to distribute this height over several steps so that excessively abrupt cross-sectional changes are avoided. The depth of the steps is to amount altogether to 3 to 10 mm.
By an appropriate form of the welding electrode abutting on the fiber side, it is achieved that the fiber structure-electrode framework compressed in the stepped area attains the full thickness up to the end of the step in an approximately continuous manner. As a result thereof, it is achieved in combination with the stepped current lug that the electrode framework is not excessively constricted at the end of the current lug and therewith cracks in the fiber framework are avoided at this place. This leads to an improved mechanical stability of the welded connection. It is additionally advantageous for avoiding fiber cracks to round-off the step edge.
Metallized plastic fiber frameworks, especially felts, needle felts, fleeces and the like are used as electrode frameworks. The metallization takes place according to the customary techniques whereby especially nickel or copper is used as metallic coating on the fibers. The plastic materials suitable also for textile fibers can be used as material for the fibers of the present invention, for example, polyolefins, polyamides, polyacrylnitriles, etc. insofar as they are stable with respect to the electrolytes with which they are to come in contact later on.